Pick-up coil should have approx 270 ohms across the terminals(disconected from harness). Ignition box needs approx 12 volts on lightblue/yellow wire. I don't think its a wiring issue if it's temp related. Box or pick-up coil. Check the pick-up coil when it's quit (most likely will be open). If its good I'd bet it's the box. I've seen them both fail with temp change. Could also be the ignition coil but I would bet against it.
Doug